Coded track circuit signaling system



Aug. 25, 1953 Filed Aug. 19, 1948 IATR w. H. REICHARD 2,650,295

CODED TRACK CIRCUIT SIGNALING SYSTEM 6 Sheets-Sheet l ZAER INVE TOR.

' A'TTORNEY 1953' w. H. REICHARD 2,650,295-

CODED TRACK CIRCUIT SIGNALING SYSTEM iled Aug. 19, 1948 6 Sheets-Sheet 2v v INVENTOR:

ATTORNEY Aug. 25, 1953 w. H. REICHARD CODED TRACK CIRCUIT SIGNALINGSYSTEM 6 Sheets-Sheet 3 Filed Aug. 19, 1948 ATTORNEY I fi m. E m fi V wm w. u m u n. m n v. w u ax I has; 3 l R I. u u Ema T u 533 I H H r lllll I llll A H hm Aug. 25, 1953 w, H. REICHARD I ,6 ,2

CODED TRACK CIRCUIT SIGNALING SYSTEM Filed Aug. 19, 1948 v 6Sheets-Sheet 4 IN V EN TOR.

BYWMMM FlGhlD;

4 ATTORNEY Patented Aug. 25, 1953 CODED TRACK CIRCUIT SIGNALING SYSTEMWade H. Reichard, Rochester, N. Y., assignor to General Railway SignalCompany, Rochester,

Application August 19, 1948, Serial No. 45,093

6 Claims. 1

This invention relates to coded track circuit signalling systems forrailroads, and it more particularly pertains to such systems whereintrack circuit coding apparatus is normally inactive but is automaticallyinitiated for the respective track sections or blocks as a trainprogresses.

A system of this type is disclosed in my prior application Ser. No.567,995, filed December 13, 1944, and the present invention is to beconsidered as providing improvements in the systems disclosed in thatapplication, and no claim is made herein to that which is disclosed inmy prior application.

In systems of the character of my above mentioned prior application andof the present invention, a stretch of track is divided into blocks bythe usual insulated joints and a signal is provided for governingentrance to each of the blocks for a given direction of trafiic. Each ofthe blocks is normally energized by steady energization from itsentrance end, and the presence of this steady energy maintains a drivencode transmitter at the exit end of that block normally inactive. Uponapproach of a train, a tumble-down of the condition of normalenergization is initiated for the respective blocks in advance and suchtumble-down is arrested after initiating coding in a predeterminednumber of blocks ahead of the train so as to permit the clearing of thesignal the train is approaching. As a means for limiting the propagationof starts to a predetermined number of blocks in advance of a train,distinctive conditions of energization such as inverse code of aselected polarity are applied at the entrance end of each of thesepredetermined number of blocks as a means for arresting the tumble-downoperation at the proper point. In order that there may be time forinverse code to become established for the purpose of arresting thetumble-down, the rate of tumble-down from block to block is governed soas to allow time for the arresting means to become effective subsequentto initiation of the coding in each block before coding in the nextblock in advance is initiated.

An object of the present invention is to initiate the propagation ofstarts for another block in advance each time that a train enters ablock, and thus suflicient coding is established to permit each signalto indicate clear upon acceptance by a train of the next signal in therear. To accomplish this mode of operation for three indicationsignalling, coding must always be active for the next two unoccupiedblocks in advance of a train.

Another object of the present invention is to limit the propagation ofstarts of coding in the respective blocks to two unoccupied blocks inadvance of a train by transmitting an inverse code of one polarity inthe first of the two blocks from the entrance end, and transmitting aninverse code of the opposite polarity in the second of the two blocksfrom its entrance end.

Another object of the present invention is to initiate coding in a blockeither by shunting or removing steady or inverse code energization inthe block in the rear, but not until after a predetermined time intervalsuch as is sufficient for arresting the propagation of the initiation ofthe coded track circuit apparatus.

Another object of the present invention is to render the approachlighting of each signal responsive to the entrance of a train into theblock immediately in approach thereof, but not until after sufficienttime has elapsed to permit the building up of code to clear that signalsubsequent to initiation of coding in another block in advance. It isthus provided that the entrance of a train into a block both initiatescoding in another block in advance and provides approach control for thesignal immediately in advance, but the approach energization of thesignal is delayed, until the code rate has had time to increase to aclear signal control rate in accordance with the coding having beenrendered eii'ective in another block.

Other objects, purposes, and characteristic features of the presentinvention will be in part obvious from the accompanying drawings, and inpart pointed out hereinafter in the specification and claims.

In describing the invention in detail, reference will be made to theaccompanying drawings in which parts having similar structuralcharacteristics and functions are designated by similar letter referencecharacters, generally made distinctive by preceding numerals indicativeof the respective signals or blocks with which such parts are moredirectly associated, and in which;

Figs. 1A to 1D inclusive, when placed end to end respectively,illustrate one embodiment of the present invention as applied to atypical stretch of track provided with three indication signalling for asingle direction of traffic; and

Figs. 2A to 2G inclusive illustrate by track diagrams and sequencecharts the coded track circuit conditions that are set up and the modeof operation that is involved under specific typical operatingconditions to be encountered in practice.

The system is illustrated by schematic wiring diagrams which are usedmore particularly to facilitate the disclosure of the invention as toits general organization and mode of operation than to illustrate thespecific construction and arrangement of parts that would be employed inpractice. The symbols and are used to indicate connections to therespective positive and negative terminals of batteries or othersuitable sources of direct current.

With reference to Figs. 1A to 1D inclusive, a typical portion oftrackway for this embodiment of the present invention is illustrated asbeing divided into blocks 2T, 3T, QT, and ET by suitable insulatedjoints. The track section H. at the left-hand end of the trackway isprovided as a starting track section and it may be a part of theautomatic signalling territory, or it may be included as part of aninterlocking organization or yard from which. entrance to the trackwaymay be made in accordance with particular conditions to be encounteredin practice.

Signals 2, 3, ii, and dare provided for overning entrance to the tracksections 2T, 3T, 4T, and ET respectively. Although thcsigna-lsillustrated are of the color light type having individual red, yellow,and green light units for providing re spective danger, caution, andclear signal indications, it is to be understood that other conven-'tional types of signals such as semaphore signals, position-lightsignals, or search light signals could as wellbe'employed in accordancewith the requirements of practice.

A coded track circuit is provided for each of the blocks 2T to 5T-inclusive, and each of the coded track circuits includes a codefollowing track'relay TR. at the entrance end of the block for receivingdriven code pulses. Respective positive and negative code followingrelays PTR and NTR are'provided in each coded track circuit at the exitend of each block for receiving inverse code pulses of respectivepositive and negative polarity. The starting track section lT has aconventional steadily'energized track circuit including a normallyenergized approach track relay lATR. Suitable direct currentenergization means is provided atjboth ends of'the respective codedtrack'cir cuit's such as the batteries which have been illustrated,separate batteries being provided at the'entrance ends of the respectiveblocks for use in selectively applying inverse code pulses of onepolarity'or the other to the'track rails. The code responsive relaysthat are included in the track'circuit are preferably of the well knownbiased polar type so as to be responsive only to energization of theparticular polarity that is intendedfor their energization. It istherefore provided by the use of relays of this character that thepositive and negative relays PTR and NTR respectively can be connectedin series in the track c'ir'cuit but with opposite polarities so thatone relay is responsive to positive energization of the track circuit,and the other relay is responsive to negative energization of th trackcircuit.

Driven code transmitting apparatus is provided at'the exit end of eachof the coded track circuits comprising suitable pulse formingoscillators lSiPCT and 'IECT for forming pulses at respective 180 and'75 rates per minutein accordance with the usual practice in coded trackcircuits. A suitable oscillator of this character which may be employedis disclosed in the patent to O. S. Field, Pat. No. 2,351,588, datedJune 20, 1944. A driven code transmitter relay CP' is associated withthe exit end of each of the coded track circuits, and such relay iseffective to transmit pulses at a selected 75 or rate when it isrendered active upon the approach of a train.

Decoding apparatus is provided at the entrance end of each of the codedtrack circuits compris ing, a decoding transformer, a home relay H, atuned decoder l ilEiDU, and 'a distant relay D. The relays D and H aremade sufficiently slow in dropping away to be steadily held up inresponse to successive pulses of the associated track relay TR, therelay I) being controlled through the tuned decoding circuit I8DDU so asto be responsive only to the reception of a 180 driven code.

An inverse code transmitter relay ACP is provided at the entrance end ofeach of the coded track ircuits for transmitting an inverse code, suchrelay being rendered active for transmission of inverse code pulsesduring the ofi periods of a driven code received at that end of theblock. Each relay is steadily energized under normal conditions to applysteady energy to the track rails of its-associated block. A relay '1? isprovided for each "of the inverse code transmitters as a means forterminating the respective inverse code pulses.

Inverse code responsive apparatus is provided at the exit end of each ofthe coded track circuits for governing the transmission of driven codesin that block and inverse codes'in the block in advance comprisingrelays 'AFP, NFP, and PEP. These'relays have slow drop awaycharacteristics so as to cause them tobe steadily picked up in responseto the pulsing of one or the other of the inverse code receiving r'elaysat'the associated end of the block. The relay AFP of this group is usedin pole changing the track circuit of the block in advance and whendeenergized thus initiates coding in that block. This relay is madesufficiently slow in dropping away to provide time for the inverse codeto be established in its associated track section to arrest propagationofstart's for the coded track circuits before its dropping away becomeseffective to initiate coding apparatus'in a block in advance. Anapproach control relay AER is provided for each of the signals as ameans or governing the energi'zation of that signal so that'it'isnormally dark,'but is illuminated upon entrance of a train into theblock immediately in approach thereof. Each of the'relays AER'hassufficiently slow drop away characteristics to permit the start ofcoding in an advance block and 'the resultant building up of code in theblock immediately in advance of the'asso'ciated signal to a 180 code sothat the energization of theassociated signal by the dropping aw'ayofthe relay AER is not eiiective prior to a change in the code rategoverning that signal as effected by the initiation of coding in anadvance block. The relative timing of the drop awaycharacteristics ofthe relays AFP and AER that is desirable will bemore'readily apparent asthe description progresses, and as reference is made to the sequence andtiming charts.

Having thus considered the general organization of the system 'for theembodiment of the present invention illustrated in Figs. 1A to 13)inclusive, consideration will now be given as to the circuitorganization in accordance with the consideration of typical modes ofoperation to be encountered'in practice.

Operation The conditions of the apparatus when it is unaffected by theapproach of a train are considered to be normal, and underthese'conditions steady energization is applied to the track rails ofthe respective blocks at the entrance ends thereof as is illustrated inthe track diagram of Fig. 2A. Thus the track rails of the block 2T (seeFig. 1A), for example, are energized with positive polarity from thebattery It! at the entrance and of the block through front contacts IIand I2 of the relays I AFP and 2ACP respectively. For the purpose offacilitating the description of the present invention the polarity ofenergization of a track circuit is considered as corresponding to thebattery connection to the upper rail in the drawings. Thus, for example,the track section 2T is said to be energized with a positive polarityunder normal conditions by the connection of the positive terminal ofthe battery It] to the top rail IS.

The relay lAFP is normally energized in accordance with the closure offront contact M of the normally energized track relay IATR for thestarting section IT; and the transmitter relay ZACP is steadilyenergized at this time in accordance with the closure of front contactl5 of relay IAFP. The steady energization of the relay IAFP under normalconditions is also effective by closure of its front contact [6 tomaintain the approach lighting control relay ZAER energized so as tomaintain the signal 2 normally dark. It will be readily apparent thatcorresponding approach control apparatus is somewhat similarlyconditioned at the entrance end of each of the blocks.

At the exit end of the block 2T, for example, the relay 2PTR is steadilyenergized in response to the positive polarity applied to the trackrails at the entrance end of that block, and the closure of its frontcontact [1, with the back contact I 8 of relay ZNTR closed, establishesa circuit for the steady energization of the relay 2AFP so that thisrelay maintains steady energy of positive polarity applied to the railsof the block 3T at the entrance end thereof through its front contact[9. It will be noted that the signals are all normally dark because ofthe normal energization of the associated approach lighting relays AER.

The negative front repeater relays NFP are normally deenergized becauseof the polarity of the steady energization being positive, and thus inaccordance with the relays NFP being deenergized and the relays AFPbeing energized, the code transmitter relays ACP at the entrance ends ofthe respective coded track circuits are all steadily energized. Forexample, the relay 3ACP is steadily energized to apply steady energythrough its front contact 31 to the track rails of the block 3T at theentrance end thereof. The circuit for the energization of relay 3ACPunder these conditions extends from (-1-), including back contact 20 ofrelay ZNFP, front contact 2| of relay ZAFP, and winding of relay 3ACP,to

For a consideration of the mode of operation of the system when a trainenters the stretch of track illustrated in Figs. 1A to 1D inclusive, itwill be assumed that a train enters the starting track section IT (seeFig. 1A) and shunts the track relay lATR so as to cause that relay todrop away and open front contact [4 which is included in the controlcircuit of the front repeater relay I AFP. The relay [AF]? in droppingaway opens its front contact [5 through which the transmitter relay ZACPhas been normally energized for application of steady energy to thetrack rails of the block 2T at its entranc end.

Thus the relay ZACP in dropping away removes energy from the block 2T bythe opening of front contact [2.

At the exit end of the block 2T, the relay ZPTR (see Fig. 1B) is droppedaway as a result of the removal of the steady energy, and this relay indropping away closes a pick up circuit for the positive back repeaterrelay 2PBP at back contact IT. The picking up of this relay establishesobvious circuits by the closure of front contact 22 for the energizationof the code oscillators 2-l80CT and 2-15CT.

The relay 2GP becomes active to transmit a 15 driven code as selected bythe relay 31-1 being deenergized. Relay 2GP is energized for each pulseof the oscillator 2-15CT by a circuit extending from including, backcontact 23 of relay ZPTR, back contact 24 of relay 2NTR, contact 25 ofoscillator 2--!5CT, back contact 26 of relay 3H, and winding of relay2GP, to Each time this relay is picked up, the closure of its frontcontact 2! connects the track battery 28 across the track rails for thetransmission of a driven code pulse. It will be noted that the positiveterminal of the battery 28 is connected directly to the top rail at theexit end of the block 2T. During each off period between the driven codepulses, the back contact 21 of the relay 2GP is effective to connect therelays ZPTR and ZNTR in series across the track rails so that the relayZPTR, is responsive to positive inverse code pulses, and the relay ZNTRis responsive to negative inverse code pulses.

At the entrance end of the block 2T (see Fig. 1A), the track relay ZTRbecomes active in response to the respective driven code pulses receivedbecause it has become connected across th track rails by the closure ofback contact I2 in accordance with the deenergization of the relay 2ACPas as been described. The pulsing of the contacts 29 and 30 of the relayZTR provides for the energization of the relay 2H through the decodingtransformer 3|, the pulsing of the contact 29 being effective toenergize the primary winding of the transformer 3| alternately first inone direction and then the other, and the pulsing of contact 39 beingeffective to commutate the output of the transformer 3i so as toenergize the relay 2H with direct current.

The relay 2H upon picking up, by the closure of its front contact 32,establishes a circuit to render the relay ZACP active for thetransmission of inverse code pulses. Thus the relay ZACP becomesenergized each time the back contact of relay 2TB is closed by a circuitextending from including, back contact [6 of relay IAFP, back contact 29of relay 2TB, front contact 32 of relay 2H, back contact 33 of relay2TP, back contact [5 of relay IAFP, and winding of relay 2ACP, to At thesame time the relay 2'I'P is energized through the inductance 34, butthe energization of the relay ZTP through the inductance 34 delays thepicking up of the relay 2TP until the desired time for termination ofthe inverse code pulse. Thus each inverse code pulse is terminated bythe opening of front contact [2 of relay 2ACP in response to thedeenergization of relay 2ACP by the opening of its circuit at backcontact 33 when the relay 2TP becomes picked up. The pick up circuit forthe relay ZTP extends from (-1-) including, back contact [6 of relayIAFP, back contact 29 of relay 2TB, front contact 32 of relay 2H,inductance 34, and winding of relay 2TP, to It will be noted that theinverse code pulses transmitted at the entrance end of the block 2T atthis time are of negative polarity because the relay IAFP is droppedaway, and thus the contact H selects the battery 35 rather than thebattery it for connection across the track rails during each inversepulse. The negative terminal of the battery 35 is connected to the upperrail of the block 2T under these conditions, and thus an inverse code ofnegative polarity is transmitted.

The reception at the exit end of the block 2T of the inverse code pulsesof negative polarity renders the relay ZNTR (see Fig. 113) active inresponse to the respective pulses, and the pulsing of front contact H!of that relay maintain relay QAFP in its picked up position and thusmaintains positive polarity applied to the track rails of the block 3Tfrom the battery 36.

The pulsing of contact 2 1 of relay 2'N'IR causes the picking up of thenegative front repeater relay ZNFP, and the picking up of that relay iseffective by the opening of its back contact 20 to remove the steadyene'r'gization from the relay SACP which is associated with the entranceend of the block ET. The relay 3A0? thus becomes dropped away and opensits front contact 3-? to remove the steady energy from the block 3T andthus initiate the transmission of driven code from the exit end of thatblock.

With reference to Fig. 10', the relay 3PTR; is dropped away upon removalof steady energy in the block 3T, and the dropping away of that relayi's eiiective by the closure of its back contact 38 to energize therelay 3P3? and thus in turn initiate the coders 3"l8'EiCT and 3-? 5CT bythe closure of front contact 39. With the oscillators initiated and withrelay SPTR' deenergized, the relay 3GP becomes active to pulse its frontcontact til for the transmission of a '55 driven code. RelaytCPisenergized for each pulse under these conditions by a circuitextending from (-l'-) including, back contact t I. of relay 3PTR, backcontact i! of relay SNTR, contact 43' of oscillator 3-15CT, back contact4 3 of relay' iH, and winding ofrelaytCP; to

The reception at the entrance end of the block 3T (see Fig. IE.) or theit driven code is eliective to pick up the relay 3H in a mannercomparable to that which has been described ior'the picking up of relayin at the entrance end of the block 2T; and the picking, up of. relay 3Hrenders. the

relay SACP active to transmit inverse code pulses. Relay 3'ACP isenergized for each inverse cod'e pulse under these conditions by acircuit extending from including, front contact titi'ofrelay ZNFP, backcontact i-S of relay 3T1t. frontcontact ll ofrel'ay 3H, back contact613' of relay STP, front contact 20 orrelay' ENFP; front contact 2! ofrelay EAFP', and Winding of relay' 3ACP, to Because of the relay beingmaintained' picked up at signal 3', the closure of. its front contact [9provides that the inverse code pulses applied to the entrance end of thetrack circuit for the block- 3T areof positive. polarity. The receptionof this inverse code. of positive polarity at the exit end of the BlochS'Tmainta'ins the relay (see Fig. 1C) picked up' to" apply energy ofpositive polarity to the entrance end; of the block Q'Tby' the. pulsingof'contact'38 of relay tPTR, and the pulsing ofthis' contact is also"effective' to maintain the positive backrepe'ater relay SPBPsteadiliy.picked upso as to maintainthe cod'e oscillators and" the driven code.transmitter relay 3GP active for transmission of a '75. code.

Because of; theslow, drop. away characteristics of the relay SAFP; thisrelay has been maintained picked up during the time required to initiatethe inverse code transmitter for the block 3T subsequent to the removalof steady energy from that block so as to prevent further propagation ofcoded track circuit starts until the polarity is changed in the block3T. In other words, with the relay BAFP maintained picked up, thepicking up of the relay SNFP is required in response to negativeenergization of the block 3T at its entrance end in order that thesteady energiz'ation of the relay iACP, and of the block 4T, can beterminated. v

At the signal 3 (see Fig. 1B) the picking up of relay 3H in response tothe l5 driven code is effective by the shifting of its contact 26 tosubstitute the contact 19 of the oscillator 2-4860! for the contact 25of the oscillator 2l 5CT in the circuit for relay 2GP so as to increasethe code rate in the block 2T from a 7-5 driven code to a 180 drivencode. This increase in code rate is effective to energize the relay 2D(see Fig. LA) at the entrance end of the block 2T through its tunedcircuit I B'BDU' and through the decoding transformer 31 to conditionthe signal 2" to provide a green aspect when the approach lighting ofthat signal becomes effective. 7

The slow drop away approach lighting relay ZAEl-t has become deenergizedin accordance with the dropping away of the relay IAFP, but because ofthe slow drop away characteristic of the relay ZAER, it is maintainedpicked up until the code rate has had time to change from a rate to arate as has been described so that there will be no yellow aspectdisplayed by the signal 2 momentarily during the building up of the codein the lock The green lam- 3G of signal 2' is energized when theapproach lighting becomes effective by a circuit extending from 6+)-including, back contact 59 o'i'relay front contact W- of relay 2H, frontcontact 5| oi relay 2 D; and lamp 6- of signal 2, to

Having thus considered the manner in which coding is set upfor thecontrol of signal 2 when a train enters the stretch, consideration-Willnow be given to the mode of" operationthe train moves from block toblock along the traxzk way so as to always maintain cod-l ng en eetivein: two unoccupied bloc'lisin advance or: the trains The sequence ofrelay operations under' these conditions is illustrated in Fig. 2EWhile. the sequence or operations: iorthe-st'art of coding ashas beendescribed: is illustrated in-Fig- 2C. Thusit will be considered that atrain accepts: the clear indication of: signal 2 and enters the block2'1- asillustraten in. the track diagrarn of Fig. 2D; By shunting thetrack rails of the block 21, the track relay (see: Fig. 1A) is droppedaway and rendered inactive and thus the relay is d'eenergized. Thedropping away of relay 2 H is eii'e'cti'v by the shifting of his contact56 to extinguish the green la-nip G of signal 2" and energize the redlamp R of that signal accordi'ng'to the usual practice. The relay z D isalsodropped away because of the train shunt oi the" block Upon" thefailure-cf the track relay 2TH tobe responsive toflthe driven codebecause of the train" shunt, the inversecode transmitter Z ACP becomesinactive. and the negative inverse code track relay ZNT'RZ (see Fig. 1B)at the exit end ofithe'tracksection Z'Tis rendered-inactive; Because ofthe failure or? this relay to pulse its con-- tact It; the relay Z'AT'P' is deenergiz'ed and" the negative repeater" relay ZNFP becomesdeenergized because of the" failure of relay ZNIR' to pulse GOIIIJYBICtT4.

After a time measured by the drop away time of the relay ZAFP, theshifting of contact E9 of relay ZAFP disconnects the track battery 36and connects the track battery 52 in the coded track circuit for theblock 3T so as to change the polarity of energization of th block 3Tfrom positive to negative. Thus the inverse code transmitted from theentrance end of the block ST is changed to negative polarity, and inaccordance therewith, at the exit end of the block, the relay 3PTR (seeMg. 10) is rendered inactive, but closure of its back contacts 38 and a!is effective to maintain the driven code transmitter relay 3GP active bythe energization of circuits that have been described. The relay SAFP ispicked up by the negative inverse cod because the pulsing of contact 53of the relay 3NTR and the negative front repeater relay SNFP at the exitend of the block 3T is picked up by the pulsing of contact 42. Thepicking up of this relay opens the circuit which has been steadilyenergized for the relay GACP at back contact 54 and thus removes thesteady energy from the block 4T at its entrance end by the opening offront contact 55 of relay 4ACP.

At the exit end of the block 4T, the relay lPTR (see Fig. 1D) which hasbeen steadily energized. is dropped away, and the dropping away of thatrelay, by the closure of its back contact energizes the relay 4PBP to inturn initiate the oscil- 1 lators 4I80CT and 4-4501 by the closure offront contact 5?. The relay 4GP thus becomes active to transmit a 75driven code which it applies by the pulsing of contact 58 to the trackrails of the block 4T at the exit end thereof. The circuit by which therelay 4GP is energized for each pulse of the 75 code extends fromineluding, back contact 59 of relay APTR, back contact 60 of relay 4NTR,contact 6| of oscillator 415CT, back contact 62 of relay H, and windingof relay 4GP, to

It will be noted that the relay 4AFP is deenergized upon the droppingaway of the relay l-PTR by the opening of its circuit at front contact56, but because of the slow drop away characteristics of this relay itis maintained picked up until there is time for the inverse codetransmitter at the entrance end of the block 4T to be rendered active soas to pulse the relay 4PTR and thus provide intermittent energizationfor the relay AFP. Thus further propagation of starts of coded trackcircuits can be arrested by the application of inverse code of apositive polarity to the entrance end of the block 4T.

Upon receiving the '75 driven code at the en" trance end of the block4T, the relay 4TR (see Fig. becomes active, and the pulsing of itscontacts 63 and 64 provides for th picking up of relay 41-1 in a mannercomparable to that which has been described for the picking up of therelay 2H at the entrance end of block 2. With the relay 4H picked up,the relay 4ACP becomes active to transmit an inverse code of positivepolarity because of the relay 3AF'P being maintained picked up to closeits front contact 74 to select that the battery 65 is used for thetransmission of the inverse code. The circuit involved in theenergization of th relay 4ACP for transmission of the inverse codeextends from including front contact 66 of relay 3NFP, back contact 33of relay 4TB, front contact 6'! of relay 4H, back contact 68 of relayITP, front contact 54 of relay 3NFP, front contact 69 of relay 3AFP, andwinding of relay 4ACP, to

Upon the reception of the inverse code of posi- 10 tive polarity at theright-hand end of the block 4T (see Fig. 1D), the relay lPTR becomesactive to pulse its contacts 56 and 59, thereby maintaining the codetransmitter relay 4GP active for the transmission of the 75 driven codeand at the same time maintaining the relay 4AFP picked up so as tomaintain steady energization of the relay 5ACP, and thus steadyenergization is maintained for the block 5T at the entrance end thereofwith a positive polarity as selected by the front contact iii of relay4AFP.

Because of the relay 4H having been picked up by the 75 driven code inthe block 4T in advance thereof, its contact 44 is effective to selectthe contact 75 of the oscillator 3l8flCT rather than the contact 43 ofthe oscillator 3-l5CT to be effective to govern the code ratetransmitted from the exit end of the block 3T. Thus the code rate isincreased from a 75 to a rat in the block ST, and the reception of this180 code at the entrance end of that block provides for the picking upof the relay 3D (see Fig. 113) through through its tuned decoder ISBDUto condition the signal 3 for the display of a green aspect when theapproach lighting becomes effective.

Inasmuch as the block ET is considered to be shunted by the train underthe conditions being considered, the relay ZAFP has been dropped away toopen its front contact 12, and because of the slow drop awaycharacteristics of the approach lighting relay 3AER, that relay becomesdropped away at a time later that is sufiicient to permit the code rateto build up from the 75 code to the 180 code as has been described so asto pick up the relay 3D and condition the green lamp G of signal 3 forenergization. The relative drop away timing desirable for these relays2AFP and SAER is diagrammatically illustrated in Fig. 2E wherein it isillustrated that the approach lighting of the signal 3 is delayed by thesuccessive drop away times of two slow drop away relays (relays ZAFP and3AER) subsequent to the shunting of the track rails of the block 2 uponentrance of a train into that block. When the relay 3AER becomes droppedaway, the green lamp of signal 3 is energized by a circuit extendingfrom including back contact 13 of relay 3AER, front contact 15 of relay3H, front contact 16 of relay 3D, and the green lamp G of signal 3, to

As the train progresses so as to leave the track section IT unoccupiedin the rear of the train, a sequence of operations becomes effective asillustrated diagrammatically in Fig. 2G whereby steady energization isapplied at the entrance end of the block 2T in the rear of the train asa means for initiating the shutting down of the coding in the rear ofthe train as it progresses.

Thus when the train leaves the track section IT, the track relay IA'IRis picked up, and the picking up of that relay is effective by theclosure of its front contact 14 to energize the relay IAFP which in turnselects the battery 10 to be connected to the track rails of the blockET by the closure of its front contact H. The picking up of this relayalso closes an obvious circuit for the steady energization of the relayZACP at front contact 15, and the relay ZACP in turn applies steadyenergization to the track rails at the entrance end of the block 2T bythe closure of front contact I2. The closure of front contact 5 of relayIAFP restores the approach lighting relay ZAER to its normal energizedposition, and the pickin up of the relay ZAER completes the restorationto normal conditions of the apparatus of signal 2 by opening backcontact as and thus extinguishing the red lamp R of signal 2.

As the train progresses further so as to leave the block 2T unoccupied,the relay ZPTE (see Fig. 1B) is picked up by the steady energy fedthrough the track rails from the entrance end of the block 2T. Thepicking up of this relay deenergizes the relay ZPBP by opening itscircuit at back contact I! and thus renders the code oscillator 2-580CTand 2-4501 inactive by the opening of front contact 22. The picking upof relay EPTR, renders the relay 2GP inactive in accordance with theopening of back contact The closure of front contact ll of relay 2PTRreestablishes the circuit by which the relay ZAFP is normally energized,and the picking up of relay 2A1? is effective by the closure of itsfront contact 18 to select the track battery 36 as the battery fromwhich steady energization of a posi tive polarity is to be applied tothe track rails at the entrance end of the block ST. The relay ZAFP inpicking up also is efiective by the closure of front contact 2! toreestablish a circuit for the relay 3ACP which has been described asbeing steadily energized under normal conditionsv When relay 3ACP ispicked up, the closure of its front contact 3? applies energy steadilyto the track rails of the block 3T at its end of a positive polarity asselected by the front contact ill of the relay ZAFP. The approachlighting relay SAER is restored to its normally energized position bythe closure of front contact E2 of relay ZAFP, and the energization ofthis relay is eilective by the opening of back contact it to extinguishthe red lamp R of signal It will be noted that each of the decodingtransformers is deenergized under normal conditions because of therelays NFP and AFP at that signal location being energized. Thus thedecoding transformer at signal 3 is deenergized with the front contact45 of relay 2NFP open and the back contact 52 of relay ZAFP open.

Having thus described the manner in which the code transmitters are shutdown and the system is restored to its normal conditions for the block2T as it becomes unoccupied in the rear of a train, it is to beunderstood that a similar mode of operation is efiective for each of theblocks as a train progresses, and that when the system is thus restoredit is conditioned so that the subsequent approach of a following traineffects the same mode of operation as has been described for theinitiation of coding.

It will be readily apparent that in cases where a following train isrunning less than three unoccupied blocks in the rear of a train inadvance that there is no restoration to normal conditions for theunoccupied blocks in the rear of the first train as the presence of thefollowing train is effective to govern the transmission of code in theblocks in advance thereof in a manner similar to the manner which hasbeen specifically considered when considering the passage of only onetrain. If there is only one unoccupied block between the first andsecond trains, the code rate for the block in advance of the secondtrain obviously cannot build up above a '75 code rate as selected by thedeenergized relay 1-1 at the exit end of that block, and although anegative inverse code is transmitted in that block to call forinitiation of coding in a block in advance, the presence of the firsttrain in the block in advance renders that control effective only toprevent the application of steady energization in the block occupied bythe first train and com 12 ditions the entrance end of that block sothat coding will be continued in that block when becomes unoccupied bythe first train.

From the typical conditions that have been described, it will be readilyapparent that as the train enters each block, the polarity of inversecode transmission in the next block in advance is changed from positiveto negative and such change is effective to remove the steady energi-Zation from the second unoccupied block in advance and initiates thetransmission of a 75 driven code from the exit end of that block. Thereception of the 75 driven code at the entrance end of this block iseffective both to increase the code rate in the block in the rear to arate, and to initiate the transmission of an inverse code of positivepolarity in that block so as to arrest the propagation of starts forcode transmitters until the train advances another block and changes thepolarity of the inverse code transmission. Thus, generally speaking, itcan be said that when a train enters a block, it initiates coding in asecond unoccupied block in advance by changing the polarity of theinverse code in the first unoccupied block so as to pick up the negativefront repeater relay NFP at the exit end of that block and therebyremove the steady energy from the second unoccupied block. It is thecombination of lack of inverse code of negative polarity to pick up arelay NFP and the presence of inverse code of positive polarity tomaintain a relay AFP energized that prevents further propagation ofstarts for the coders of the respective blocks beyond the secondunoccupied block in advance of the train.

It is to be understood that there are a number of expedients that may beemployed for the initiation of the normally inactive coded track circuitsystem provided by the present invention, particularly at the entranceto the equipped territory. In any case, well known approach controlexpedients may be employed to fit the conditions encountered in practiceso as to clear the signal governing entrance to the territory, such asthe signal 2 of Fig. 1A. The approach control of signal 2 as illustratedin Fig, 1A is particularly adapted for low speed train movements whereonly a caution indication is required for the next signal in the rear ofthe signal 2. If, however, high speed train movements are anticipatedupon entrance to the coded track circuit equipped territory, coding inadvance of signal 2 may be initiated either manually by a toweroperator, or automatically by the entrance of a train into the secondblock in the rear of that signal so that the relay 2H can be picked upto provide for the transmission of a clear control to the next signal inthe rear of signal 2 to govern the approach of the train.

If the signal 2 is to be considered as the leaving signal of aninterlocking plant which is subject to manual control of a toweroperator, a conventional manually controlled signal control relay forthat signal can be used in place of the approach track relay IA'IR, toinitiate the coding, such signal control relay being energized when thesignal is to be cleared and being deenergized when the signal 2 is putto stop in the rear of a train. By this arrangement, a back contact ofthe signal control relay would be used instead of the front contact M ofthe relay lATR in the control of the pole changing relay IAFP.

If there is a track switch connection to the stretch of track that isequipped with coded track circuits according to the present invention,the reversal of such track switch when proper authorization for suchreversal has been granted is effective by shunting the track rails toremove the condition of steady energization of the associated block andthereby initiate coding in two blocks in advance and govern the clearingof a signal for the passage of a train subsequent to its movement out ofthe track switch. The initiation of coding under these conditions isaccomplished by a mode of operation comparable to that which has beendescribed for the initiation of coding upon the entrance of a train intothe approach track section IT.

It will be readily recognized that other means may be employed forgoverning the initiation of code transmitters for the respective blocksin advance of a train as it progresses in combination with the featureof the present invention that delays the energization of the signallamps until the code has had time to be built up to a rate for governingdisplay of the least restrictive aspect of the signal for which theapproach control is provided. Thus, this approach control feature may bereadily applied, for example, to the systems disclosed in my abovementioned prior application. It is also to be understood that the systemdisclosed in this embodiment of the present invention may be modified asrequired in practice to provide for four block signalling indications.

Havin thus described a coded track circuit signalling system for atypical stretch of track as one embodiment of the present invention, itis desired to be understood that this form is selected to facilitate thedisclosure of the invention rather than to limit the number of formswhich the invention may assume, and it is to be further understood thatvarious adaptations, alterations, and modifications may be applied tothe specific form shown to meet the requirements of practice without inany manner departing from the spirit or scope of the present inventionexcept as limited by the appending claims.

What I claim is:

1. A coded track circuit signalling system for a stretch of railwaytrack divided into blocks and having a signal governing entrance to eachblock for a given direction of traffic comprising in combination, acoded track circuit for each of the blocks having code transmitting andreceiving apparatus at each end of the associated block, said codetransmitting apparatus being normally inactive but being initiated whenits associated block is a predetermined number of blocks in advance ofan approaching train, approach control means associated with each of theblocks responsive to the presence of a train in that block forinitiating said code transmitting apparatus at the exit end of anotherblock in advance, and a slow acting approach lighting relay for each ofthe signals operable in response to said approach control means for theblock in the rear for energizing its associated signal, said slow actingrelay being effective to initially energize its associated signal uponentrance of a train into said block in the rear, only provided there hasbeen time for the initiation of coding in another block in advance inresponse to said approach control means so as to condition theassociated signal to give a clear indication when energized.

2. In a coded track circuit signalling system for a stretch of railwaytrack divided into blocks and having a signal governing entrance to eachblock for a given direction of traffic, the combination with a codedtrack circuit for each of the blocks having normally inactive codetransmitting and receiving means at each end thereof, of an approachtrack relay at the exit end of each of the blocks energized over thetrack rails by energy fed from said transmitting means at the entranceend of that block, a slow acting approach repeater relay energized bysaid approach track relay and efiective when deenergized to initiatesaid code transmitting means for another block in advance, and a slowacting approach lighting relay for each of the signal normally energizedby said approach repeater relay effective when dropped away to energizeits associated signal, said approach lighting relay being sufiicientlyslow in dropping away to allow time for initiation of coding in anotherblock in advance and for the code rate to increase as a result thereofin the block immediately in advance of that signal to its rate forgoverning the least restrictive signal indication.

3. In a coded track circuit signalling system for a stretch of railwaytrack having adjoining blocks and having a signal governing entrance toeach block for a given direction of traffic, the combination with acoded track circuit for each of the blocks having normally inactive codetransmitting and receiving means at each end thereof and having means atits entrance end for applying energy of a selected polarity, ofrespective oppositely poled approach track relays at the exit end ofeach of the blocks energized by energy fed from said transmitting meansat the entrance end of that block, a slow acting approach repeater relayenergized when either of said approach track relays is active, saidapproach repeater relay being eifective when energized to select thepolarity of energization for the track rails of the block in advance,and a slow acting approach lighting relay for each of the signalsnormally energized by said approach repeater relay and effective whendropped away to energize its associated signal, said approach lightingrelay being suiiiciently slow in dropping away to allow time forinitiation of coding in a block in advance in response to said approachrepeater relay.

4. A coded track circuit signalling system for a stretch of railwaytrack divided into blocks and having a signal governing entrance to eachblock for a given direction of traflic, a coded track circuit for eachof the blocks having code transmitting and receiving apparatus at therespective entrance and exit ends thereof, said code transmittingapparatus at the entrance ends being normally eifective to steadilyenergize the track rails with a given polarity but at other times totransmit an inverse code of a selected polarity, said code receivingmeans at the exit end comprising oppositely poled code following relaysrespectively responsive to code pulses transmitted through the trackrails of their particular polarities, a pole changing relay at eachsignal energized in response to the energization of either of said codefollowing relays and effective to select the polarity for energizationof the track rails for the block in advance, said pole changing relayalso being effective when deenergized to remove the steady energy fromthe block in advance, approach control means at each signal responsiveto the pulsing of a particular one of said code following relays forremoving steady energy from the next block in advance, and therebyinitiating coding in that block, and slow-acting approach lighting meansfor each signal effective to approach light that signal a predeterminedtime subsequent to initiation of coding in a block in advance inaccordance with the deenergization of said pole changing relay.

5. In a coded track circuit signalling system having a plurality ofnormally inactive coded track circuits for governing the indications ofrespective signals for a given direction of traffic, normally inactivecode transmitting and receiving apparatus at the respective entrance andexit ends of each of said track circuits, said code receiving apparatusat the entrance end of each track circuit comprising a code followingtrack relay and a decoding transformer having its primary windingenergized first in one direction and then the other by the pulsing of acontact of said code following track relay and having a slow-actingrelay energized by its secondary winding, and automatic initiatingapparatus for rendering said coded track circuits active in advance of atrain one at a time as the train progresses from one track circuit tothe next, said initiating apparatus being effective to maintain saidprimary winding of said decoding transformer deenergized except when atrain is within a predetermined number of track circuits of the trackcircuit with which such means is associated.

6. A coded track circuit signalling system for a stretch of railwaytrack divided intoblocks and having a signal for governing entrance toeach of the blocks for a given direction of traiiic comprising incombination, a coded track circuit for each. of the blocks having codetransmitting and code receiving apparatus at each end of the block, saidcode transmitting apparatus at the exit end being normally inactive butbeing effec 16 tive when rendered active to transmit a driven code, saidcode transmitting apparatus .at the entrance end being normallyeffective to apply steady energy of a given polarity to the coded trackcircuit of that block and being effective to remove such steady energyand apply inverse code of said given polarity during the off periods ofdriven code transmitted from the opposite end of the block in responseto a change to the opposite polarity of energy transmitted from theentrance end of the next block in the rear, said code transmittingapparatus at the exit end being rendered active to transmit a selecteddriven code in response to cessation of steady energy transmitted fromthe entrance end of that block, except when such steady energy isreplaced by the transmission of inverse code of said given polarity, andpole changing means at each signal responsive to a train shuntinginverse code transmitted from the entrance end of the next block in therear for changing the polarity of inverse code pulse transmission in thenext block in advance to said opposite polarity and thereby initiatedriven code transmission from the exit end of the second block inadvance of that signal.

WADE H. REICHARD.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 1,887,261 Failor Nov. 8, 1932 2,122,373 Hormats June 28, 19382,275,838 Blosser Mar. 10, 1942 2,335,765 Judge Nov. 30, 1943 2,519,979Preston Aug. 22, 1950

